An epoxy resin composition containing an epoxy resin and a curing agent thereof as essential components are widely used in electronic and electric components such as semiconductor encapsulation materials and printed circuit boards, conductive adhesives such as conductive pastes, other adhesives, matrixes for composite materials, coating materials, photoresist materials and developing materials because of excellent various physical properties such as heat resistance, moisture resistance and low viscosity.
In these various applications, particularly advanced materials, it has recently been required to further improve performances typified by heat resistance and moisture resistance. For example, in the field of semiconductor encapsulation materials, a reflow treatment temperature increased due to shift to surface mounting packages such as BGA and CSP and correspondence to lead-free solders, and thus electronic component encapsulation resin materials having excellent moisture soldering resistance are more required than before.
As the technique for producing electronic component encapsulation resin materials which meet such requirements, for example, there is known a technique in which fluidity is improved by using, as a curing agent for epoxy resin, a methoxy group-containing phenol resin obtained by methoxylating a phenolic hydroxyl group in a resol resin and converting the methoxylated resol resin into a novolak resin in the presence of an acid catalyst and also proper flexibility is imparted to the cured article, and thus moisture resistance and impact resistance of the cured article itself are improved (see, for example, Japanese Unexamined Patent Application, First Publication No. 2004-10700).
However, such a curing agent for epoxy resin is inferior in heat resistance because of small number of functional groups per molecule. In the field of electronic components, it is of urgent necessity to develop a high-frequency device capable of coping with higher frequency and materials having low dielectric constant and low dielectric dissipation factor are required to electronic component-related materials such as semiconductor encapsulation materials. The cured article obtained by using the methoxy group-containing phenol resin as the curing agent for epoxy resin has less crosslink points and therefore dielectric characteristics are improved to some extent, however, dielectric constant and dielectric dissipation factor do not attain the level which has recently been required.
As described above, in the field of electronic component-related materials, there has never been obtained an epoxy resin composition capable of coping with recent higher frequency without causing deterioration of heat resistance.